Key telephone system for subscribers

ABSTRACT

A key telephone system for subscribers is disclosed which includes at least a plurality of key telephone stations, a subscriber common equipment which connects the key telephone stations to each other and further connects the key telephone stations and an private automatic branch exchange, wherein said subscriber common equipment comprises switching network circuits, a register connecting circuit, line circuits, intra-office circuits, line circuit links, intra-office circuit links and a common controller, whereby each of said key telephone stations is connected to the subscriber common equipment through a pair of speech lines and a few control lines, and further said key telephone station can handle data processing services through said control lines by using a data terminal equipment attached to the key telephone station and a data processing unit by way of said subscriber common equipment.

The present invention relates to a key telephone system for subscribers.

Recent private automatic branch exchange systems include a wide varietyof numerous new services which are operated by subscribers; forinstance, transfer, call-back, pick-up, camp-on, add-on, holding,conference telephone, call-waiting, paging, abbreviated dialing,call-advance in case a called subscriber is absent, don't-disturb, ormessage services. Further, in an automatic exchange system which iscontrolled by using a stored program, the multiplication of functions ina terminal device is greatly advanced, and thereby in resent years thenecessity to carry out many of the aforesaid services is remarkablyincreasing.

As mentioned above, the automatic exchange system has made greatadvances, and various new kinds of services have been introducedtherein. However, most of the telephone stations which are currentlyused, are still old-fashioned. Only a service button (gland button) fordemanding services, if anything, is used in a limited number oftelephone stations of subscribers, where the demand and release of theaforesaid new services are effected, in most cases, by the operation ofa handset or by dialing a special number. Accordingly, complicatedoperations are required for subscribers who utilize the new servicesusing conventional telephone stations and, hence, such new services arevery difficult to utilized.

Consequently, in recently years, there is a remarkably strong demand notfor the aforesaid conventional telephone stations but for the keytelephone stations. One of the factors behind this may be the easinessof operation of the key telephone stations, when compared to theoperation of the aforesaid conventional telephone stations. The keytelephone system is often used in such a manner that it is incorporatedinto extensions in the form of a number of relatively small keytelephone systems mounted in a private automatic branch exchange.

However, if one tries to utilize the aforesaid many services by using aconventional key telephone system, each key telephone station isrequired to have many connections to various lines; such as a pluralityof telephone line circuits, a plurality of control wires of the flickerlamps for indicating the condition of the each telephone line circuit, aplurality of control wires for various service functions, power sourcelines for providing electric power to the electronic circuits mounted inthe key telephone station, and so on. For instance, in a key telephonesystem having 20 central office lines, each key telephone station of thekey telephone system will be required to have thirty buttons and a fewhundred lead wires and, as a result, such a key telephone station willbecome as large as an attendant board; in addition, the operation of thekey telephone station will become too complicated when it is usedpractically. Since the key telephone station would have 30 buttons and afew hundred lead wires, it is very difficult to expand the capacity ofthe line circuit and it is very costly, and takes considerable time tomaintain the key telephone system further, there is an excessivecomplexity in lead wire connections.

It is a principal object of the present invention to provide a uniquekey telephone system in which each key telephone station can deal withall of the aforesaid new services without increasing the number ofbuttons and lead wires which would be increased when the conventionalkey telephone station is used. Furthermore, the key telephone system ofthe present invention can deal with not only the aforesaid new servicesbut, also, data processing services without interrupting the operationof the aforesaid new services.

The present invention will be more apparent from the ensuing descriptionwith reference to the accompanying drawings wherein:

FIG. 1 is a block diagram showing an example of a conventional keytelephone sytem;

FIG. 2 is a block diagram of a key telephone system according to thepresent invention;

FIG. 3 is a block diagram of a switching network circuit;

FIG. 4 is a block diagram of a line circuit;

FIG. 5 is a schematic diagram showing the structural arrangement of aspeech-path network according to the present invention;

FIG. 6 is a block diagram of a common controller;

FIG. 7 is a graph showing an example of scanning time slots;

FIG. 8 is a block diagram of a key telephone station according to thepresent invention;

FIG. 9 is a diagrammatic illustration of the appearance of a keytelephone station according to the present invention;

FIG. 10 is a block diagram showing a total view of a data exchangesystem according to the present invention;

FIG. 11 is a block diagram showing the modified switching networkcircuit shown in FIG. 3 which further includes a part of the dataexchange system, according to the present invention;

FIG. 12 is a block diagram showing the modified key telephone stationshown in FIG. 8 which further includes a part of the data exchangesystem, according to the present invention; and

FIG. 13 is a block diagram of a data terminal equipment according to thepresent invention.

FIG. 1 illustrates an example of conventional key telephone systems. InFIG. 1, KTSU represents a main unit of a conventional key telephonesystem, and KSA₀ through KSAn and KSB₀ through KSBn representconventional key telephone stations each of which has buttons and lampsboth of which connect to corresponding telephone line circuits. Aplurality of telephone line circuits are connected to each of the keytelephone stations in a multiple fashion. The selection of one of theplural telephone line circuits is carried out by using a button mountedthereon which corresponds the one of the plural telephone line circuits,and flicker lamps mounted on each of the key telephone staions indicatethe telephone line circuit condition selectively, such as busy, held andcalled. In order to satisfactorily operate such a communication systemas mentioned above, each key telephone station is required to have manyconnections to various lines; such as a plurality of telephone linecircuits, a plurality of control wires of the flicker lamps forindicating the condition of the each line circuit, a plurality ofcontrol wires for various service functions, power source lines forproviding electric power to the electronic circuits mounted in the keytelephone station, and so on. As a result, a considerably large numberof wires must be connected between each of the key telephone stationsand the main unit. In FIG. 1, CO represents a central office or aprivate branch automatic exchange, and S represents a currently usedtelephone station.

At the present, due to continuing tecnical and sociological advancesincreases are required in the capacity of communication systems as wellas availability of new kinds of services, easy installation andmaintenance, and reduction of the size of the total equipment in use.However, with the conventional key telephone systems, any increase incapacity and any addition of service functions, result in a requirementfor a great deal more line connecting buttons, service buttons and leadwires.

The present invention mitigates the aforesaid difficulty of theconventional technique in a key telephone system. With the key telephonesystem according to the present invention, the selection of thetelephone line circuits is carried out by switching network circuitsinstalled within a subscriber common equipment. The subscriber commonequipment corresponds to the conventional main unit of a key telephonesystem (shown as KTSU in FIG. 1). That is, the key telephone station ofthe present invention does not have any buttons which connect tocorresponding telephone line circuits, and said selection of the links,for example line circuit links, intra-office circuit links, registerlinks, ringing tone link, and busy tone link, is effected by dialing.The dial information caused by dialing is delivered to the subscribercommon equipment in a form of pulse signals through a control lineconnected between the key telephone station and the subscriber commonequipment and, then, the subscriber common equipment counts the pulsesignals and thereby selects the desired telephone line circuit. When thesubscriber common equipment converts the dial information, that is thepulse signals, into a push-button signal (DTMF: dual tonemulti-frequency address signal) which is a so-called PB signal, the PBsignal is turned back to the key telephone station which is beingoperated. At the same time, when the desired line circuit is selected,the PB signal is also sent to the desired line circuit. Further, the keytelephone station of the present invention is equipped with anintra-office originating button and an intra-office receiving button. Incase a call is originated by pushing the intra-office originatingbutton, an idle intra-office line circuit is automatically selected, andin case a call is received, a telephone line circuit is formed throughan idle intra-office line circuit by pushing the intra-office receivingbutton. With the aforesaid arrangement, the buttons to be mounted on thekey telephone station of the present invention become only dial buttons,an intra-office originating button, an intra-office receiving button, aholding button, and a few option buttons. Moreover, according to thepresent invention, the individual telephone station does not have anyconventional push-button signal oscillator which is a so-called PBoscillator but, rather, a few PB oscillators are installed in thesubscriber common equipment for common use by a number of key telephonestations. Thereby, the size of the key telephone station is reduced, theoperation of the telephone station is improved. And further theconventional push-button signal receiver, which is a so-called PBreceiver, is not required. The PB receiver has been necesary in aconventional key telephone exchange using a PB telephone station.Furthermore, the number of cables can be reduced to a few cables per keytelephone station, and this allows simplification of the installation ofthe key telephone system and its maintenance. In addition, the presentinvention uses control lines between the key telephone station and thesubscriber common equipment. The control lines are provided not only fortransmission of the data necessary for processing at the telephoneexchange, but also for transmission of the data used for operation ofdata processing, if necesary. The operation of data processing throughsaid control lines will offer various kinds of new services to thesubscribers who utilize the key telephone system according to thepresent invention.

The invention will now be described in detail by referring to theaccompanying drawings. The overall key telephone system according to thepresent invention, is shown in FIG. 2, and details of various devices inthe overall key telephone system are shown in FIG. 3 through FIG. 6 andFIG. 8 through FIG. 13.

Referring to FIG. 2, CE represents a subscriber common equipment whichcorresponds to the key telephone main unit of the prior art, shown asKTSU in FIG. 1. The subscriber common equipment CE, which is surroundedby a chain line, consists of the following devices. As shown in FIG, 2,one type of device is a switching network circuit SNC, of which thereare a plurality. Each SNC is arranged to a corresponding key telephonestation ST and is connected to the corresponding key telephone stationST through a few, for example four, control lines CL and two speechlines SL. The details of the switching network circuit SNC is shown inFIG. 3 surrounded by a chain line. As shown in FIG. 3, the switchingnetwork circuit SNC comprises: a shift register SR₁ which stores controlinformation sent from a common controller CC shown in FIG. 2, where thecontrol information indicates which telephone line circuit has to beselected among a plurality of telephone line circuits; a connectingnetwork CNW which connects the selected telephone line circuit to adesired line circuit link or an intra-office line circuit link, based onthe control information which is stored in the shift register SR₁ ; abalance-unbalance converter circuit BUC which converts a part of aspeech-path circuit from a balanced circuit to an unbalanced circuitand, at the same time, provides a speech-carrying current to thetelephone station ST; a data driver circuit CD₁ which sends lamplighting information to the key telephone station ST; a data receivercircuit CR1 which receives lamp information for indicating the conditionthe telephone line circuit from the key telephone station, and; a datagate circuit DG which controls the lamp lighting information and thelamp information to be processed.

The details of a line circuit LC of FIG. 2 are shown in FIG. 4surrounded by a chain line. As shown in FIG. 4, the line circuit LCcomprises: an unbalance-balance converter circuit UBC which converts thelines between the switching network circuit SNC and the key telephonestation ST from an unbalanced circuit to a balanced circuit; a loopholding circuit LHC which forms a D.C. loop between the line circuit LCand the central office system or automatic exchange system CO when theline circuit LC is operating; a ringing detector circuit RC whichdetects ringing signals when the line circuit LC is called, and; a loopcut detector circuit LCC which detects a break of the D.C. loop on thelines between the line circuit LC and the central office system orautomatic exchange system CO.

The details of a register connecting circuit RGC of FIG. 2 are alsoshown in FIG. 3. Referring again to FIG. 3, the register connectingcircuit RGC comprises the shift register SR1 a connecting network CNWand the data gate circuit DG. The connecting network CNW is connected toa PB (push-button) oscillator PBOSC which is shown in FIG. 5. Accordingto the present invention, all the dialing is effected by push-button,and the PB oscillator PBOSC is not disposed in the telephone station STbut in the common controller CC. The register connecting circuit RGCconnects the PB oscillator PBOSC to one of the desired line circuitlinks LCL₀ through LCLn (shown in FIG. 5) or one of the desiredintra-office circuit links ICL₀ through ICLN (shown in FIG. 5) to whichthe switching network circuit SNC of the originating key telephonestation ST is connected. As a result, a PB signaling tone from the PBoscillator PBOSC is sent out to both the key telephone station ST andthe central office CO, in response to the dial information sent from thekey telephone station ST. Said dial information sent from the keytelephone station ST is applied to the common controller CC through thecontrol lines CL and information lines P₂ and P₃, as shown in FIGS. 3and 6. As a result, the common controller CC drives the PB oscillator inaccordance with the dial information.

A network of the speech-path portion according to the present inventionwill now be described by referring to FIG. 5. In FIG. 5, the telephonestations ST, the line circuits LC, the intra-office circuits IC, theswitching network circuits SNC, the register connecting circuit RGC andthe common controller CC, are the same as those of FIG. 2. Further, theconnecting network circuit CNW and the balance-unbalance convertercircuit BUC are the same as those of FIG. 3. Block RT represents aringing tone transmitter and block BT represents a busy tonetransmitter. As shown in FIG. 5, the key telephone stations ST and thePB oscillator PBOSC of the common controller CC are arranged along ahorizontal line of a network, where the PB oscillator PBOSC provides adial tone DT and PB signal tone PB, selectively by means of a switchCN₃. The line circuits LC, the intra-office circuits IC, the ringingtone transmitter RT and the busy tone transmitter BT are arranged alonga vertical line of the network. Furthermore, the network includes aplurality of register links RL₀, RL₁ . . . which connect the PBoscillator PBOSC to the key telephone station ST. It should be notedthat the network arrangement of the speech path portion is notrestricted to that of FIG. 5, but various modifications are possible;for instance, the vertical connections and the horizontal connections ofFIG. 5 can be interchanged. The switching arrangement of the network isnot restricted to that of FIG. 5 either. The connecting operation of thenetwork shown in FIG. 5, will be discussed hereinafter.

The common controller CC of FIG. 2 controls the successiveinterconnection of the line circuit LC, the switch network circuit SNCand the register connecting circuit RGC, in accordance with a series ofprograms. The details of the common controller CC will now be describedby referring to FIG. 6. In FIG. 6, TM represents a timing signalgenerator which produces clock signals. The clock signals are applied toa decoder DR₁, so as to produce scanning signals which are directed tospecifying one of the switching network circuits SNC sequentially. Forinstance, each of the scanning signals specifying the switching networkcircuit SNC has a period of 500 μs, as shown in FIG. 7; that is, thespecified switching network circuit SNC cooperates with a correspondingkey telephone station ST every period of 500 μs. Since eighty keytelephone stations ST are arranged in the preferred embodiment of thepresent invention, a scanning period of 40 ms = 500 μs × 80) is allowedfor scanning all the switching network circuits SNC. The scanningsignals are applied to the switching network circuit SNC of FIG. 3through the scanner lines so shown in FIGS. 3 and 6, respectively. Thescanning signal on the scanner line SO, causes information to be appliedto the specified switching network circuit SNC as an input thereof. Suchinformation includes information to be applied to the shift register SR₁(FIG. 3) from a clock signal line R₁ (FIGS. 3 and 6), a reset signalline R₂ (FIGS. 3 and 6), and control lines CCL₀ through CCL₄ (FIGS. 3and 6). These control lines deliver information comprised of 5 bits,which indicate which link has to be selected among a plurality of links,LCL₁ through LCLn, ICL₁ through ICLn, RL₀, RL₁, BL and RL. In addition,said information further includes information which is sent to the keytelephone station ST through the information lines P₀ and P₁ (FIGS. 3and 6), that is lamp information. Also, said information includesinformation which is sent from the key telephone station ST throughinformation lines P₂ and P₃ (FIGS. 3 and 6), that is the informationoriginated by dial buttons, the intra-office originating button,intra-office receiving button, holding button, and so on. Said scanningsignals on the scanner line SO cause the reading of a service classinformation with respect to each of the key telephone stations, from aservice class information memory ROM (FIG. 6). Such service classinformation relates to the key telephone being scanned. The shiftregister SR₁ of FIG. 3 can handle input/output signals both in paralleland in series, and the stored information of the shift register SR₁ istransmitted to a receiving register RCR of FIG. 6 through the data gatecircuit DG (FIG. 3) and the information line P₃ (FIGS. 3 and 6). Itshould be noted here that the information line P₃ carries not only th PBbutton information from the key telephone station ST through the datareceiver circuit CR₁ and the data gate circuit DG but, also, the storedinformation of the shift register SR₁ through the data gate circuit DG.Thereafter, the stored information of the shift register SR₁ is appliedonce again into this shift register SR₁ in series. In the systemaccording to the present invention, the time required for the abovere-application of the stored information to the shift register SR₁ isrelatively short, and during this short time the connecting network CNWwhich consists of conventional relays can not operate. Consequently, abuffer register is required at the input stage of shift resistor SR₁ tohold the stored information momentarily.

Referring still to FIG. 6, a register R stores information whichindicates which line circuit links LCL₀ through LCLn or whichintra-office circuit links ICL₀ through ICLn is occupied by the keytelephone station ST being scanned. Based on the decoded information, bya decoder DR₂, from the register R, lamp flickering signals (i.e.,called engaged, held) of each telephone line circuit are applied to alamp lighting control circuit LPC, so as to prepare the line informationto be sent to the key telephone station being processed. At the sametime, other information for the key telephone station ST being processedis also prepared. This information includes a power source throw-insignal for an amplifier AMP (FIG. 8) of the key telephone station ST,status signals of intraoffice lines, and lamp information for optionbutton lamps. The information thus prepared is applied to an outgoingsender register OSR and, then forwarded to a gate circuit GC by serialclocks. The gate circuit GC extracts both level 1 signals and level 0signals as level 1 signals, and, then, sends the level 1 signals to theswitching network circuit SNC through the information line P₀ in theform of level 1 signals and sends the level 0 signals to the switchingnetwork circuit SNC through the information line P₁ in the form of level1 signals. The information both on the information lines P₁ and P₀,indicates the lamp information. The signals which are provided throughthe line P₀ (FIG. 3) and indicate the lamp information, are furtherdelivered to the key telephone station ST by the data driver CD₁ of FIG.3 through the control lines CL of FIG. 3, in the form of bipolar pulseshaving positive pulses and negative pulses.

The details of the key telephone station ST will now be described byreferring to FIG. 8. The first bit of the data which are sent over thecontrol line CL by way of a data receiver circuit CR₂, acts not only asa clock for applying various button information to a shift register SR₂in parallel but, also, as a power throw-in signal for an amplifier AMPwhich drives a speaker SP to radiate a ringing tone. Said first bit isstored in a flip-flop F/F2, so as to hold the amplifier AMP active ornon-active. The second and the succeeding bits of the aforesaid datawhich are sent over the control line CL by way of the data receivercircuit CR₂, are transferred into a shift register SR₃ as lampinformation and, at the same time, such bits act as clock pulses for theshift register SR₂. The stored button information in the shift registerSR₂, are converted into bipolar pulses by a data driver circuit CD₂.These bipolar pulses are transferred to the data receiver circuit CR₁(FIG. 3) of the switching network circuit SNC through the control lineCL. The signals sent from the data receiver circuit CR₁ (FIG. 3) areseparated by the data gate circuit DG (FIG. 3) into level 1 signals andsynchronizing signals. The separated level 1 signals are applied to theinput terminal of the receiving register RCR (FIG. 6) through theinformation line P₂ (FIGS. 3 and 6), while the separated synchronizingsignals are applied to the clock terminal of said receiving register RCRthrough the information line P₃ (FIGS. 3 and 6).

A pulse error check of the button information provided from the keytelephone station is an important function for preventing erroneousoperations. Although various methods have been used heretofore forchecking pulse error of the button information, in the present inventionthe checking pulse error of the button information sent from the keytelephone station ST is performed by counting the number of pulses ofthe button information, where the number of pulses of the buttoninformation is predetermined. The dispatching of the data from the keytelephone station ST is clocked by each lamp information sent to the keytelephone station ST and, accordingly, one bit of lamp information canbe received by the station ST every time one bit of button informationis sent out from the station ST, synchronous with the period oftransmitting each lamp information, for example 500 μs in FIG. 7.Information error which would occur on the transmission lines is causedeither by disappearance of the information or by disappearance ofinformation where there is no actual information. In the presentinvention, since the level 1 pulse is represented by a positive pulseand the level 0 pulse is represented by a negative pulse, informationerror which is caused by a change of positive pulse to negative pulseand vice versa, can not occur. That is, the number of pulses of thebutton information which is sent from the key telephone station ST iscounted by a counter CT (FIG. 6), and the error check is carried out bycomparing the counted number of pulses of the button information and thepredetermined number of pulses of the button information at an errorcheck circuit EC (FIG. 6). The button information sent from the keytelephone station ST is the ON-OFF information of the hook switchactuated by a handset H (FIG. 9), the function button information (theinformation relating to the intra-office originating button, theintra-office receiving button, or the holding button), the informationrelating to the option buton, or the information relating to thepush-button dial (dial information). The hook switch information whichindicates that the hook switch is actuated by the handset H (FIG. 9) andis held ON, is collated with the hook switch information which has beenstored in a random access memory RAM (FIG. 6), by a hook up detector HUD(FIG. 6), so as to detect an originating call or the completion of acall. In this case, when an error is noticed by the information providedfrom the aforesaid error check circuit EC, priority is given to theinformation which has been stored in the memory RAM, so as not to effectany change in the preceding conditions. This is to prevent breakage ofthe line circuit during a conversation and two times or more detectionof the same originating call.

The appearance of a key telephone station ST according to the presentinvention will be now described by referring to FIG. 9. In FIG. 9: thesymbol H represents a handset; PB represents push-button dials; SPrepresents a loud speaker which radiates a ringing tone; LP representslamps displaying the condition, for example busy, idle, called or held,of each line circuit; PLP represents lamps displaying the condition, forexample busy, idle called or held, of each intra-office circuit; OPBrepresents lamps displaying option buttons each of which provides theaforesaid various kinds of new services; OPBL represents two lamps, oneof which indicates whether one of said option buttons is being operated(add-on) and another of which indicates whether a don't-disturb functionis being operated; HLD represents a holding button; INTR represents anintra-office receiving button, and; INTO represents an intra-officeoriginating button.

The operation of above-mentioned various kinds of buttons and theconnections of these buttons to the electronic circuits, will now bedescribed in a sequential fashion. When the handset H is raised, hookswitch information representing such hook-up is written in the shiftregister SR₂ of FIG. 8. This hook switch information is then transferredto the data gate circuit DG of the switching network circuit SNC of FIG.3 by the data driver circuit CD₂ (FIG. 8) through the data receivercircuit CR₁ (FIG. 3). The signals sent from the data receiver circuitCR₁ (FIG. 3), are separated by the data gate circuit DG (FIG. 3) intodata signals and synchronizing signals. The separated data signals areapplied to the input terminal of the receiver register RCR (FIG. 6)through the information line P₂ (FIGS. 3 and 6). The separatedsynchronizing signals are applied to the clock terminal of saidreceiving register RCR (FIG. 6) through the information line P₃. Whenapplication of the above-mentioned data signals and synchronizingsignals to the receiving register RCR is completed, the hook up detectorHUD compares the hook switch information thus received against thecorresponding past information which has been stored in the memory RAM(FIG. 6), and; the origination of a call is detected by finding out thefirst appearance of the hook switch information in the receivingregister RCR. A control circuit CONT (FIG. 6) selects an idle countercircuit COU (in FIG. 6 only one counter circuit COU is shown) and anidle register link (shown as RL₀, RL₁ . . . in FIG. 6). In order toconnect the thus selected register link to both the switching networkcircuit SNC of FIG. 3 and the register connecting circuit RGC of FIG. 5,the information which commands this connection is sent out from thecontrol circuit CONT of FIG. 6 in a form of a binary code through thecontrol lines CCL₀ through CCL₄ (FIGS. 3 and 6) and, then, theinformation is stored in the shift register SR₁ (FIG. 3). Theinformation thus sent and stored, acts to close corresponding switchesin the connecting network CNW of FIG. 5. For instance, when the switchesCN₁ and CN₂ are closed and the switch CN₃ is turned to the right, asseen in FIG. 5, then the dial tone DT is sent to the key telephonestation ST₀ through the register link RL₀. When the dial tone DT isheard from the handset H of the key telephone station ST₀, thesubscriber pushes the intra-office originating button, INTO of FIG. 9,when he wants an intra-office call. The information originated by theintra-office button INTO is applied to the shift register RCR of FIG. 6in the same manner the aforesaid hook switch information is applied tothe shift register RCR. The control circuit CONT selects an idleintra-office circuit IC in the same manner as the aforesaid selection ofthe register link. For instance, when the switches CN₄ and CN₅ of FIG. 5are closed while the aforesaid switches CN₁ and CN₂ are opened, the idleintraoffice circuit is selected by way of the intra-office circuit linkICL₀ of FIG. 5. When the subscriber, who occupies the station ST₀ ofFIG. 5, hears the dial tone DT, he knows that the station ST₀ isconnected to one of the intra-office circuits which providespeech-carrying current and, then, he starts dialing a desiredintra-office key telephone station number. Th counter circuit COU (FIG.6) stores two digits of the dial information and, at the same time, thisdial information drives the PB oscillator circuit PBOSC (FIG. 6), so asto return the PB oscillator signals to the originating subscriber. Thenumber counted by the counter circuit COU (FIG. 6) is stored at theaddress in the memory RAM which corresponds to the proceedingintra-office circuit.

With regard to the connection to the called subscriber, when the calledkey telephone station finds its own number in the memory RAM, thetelephone line circuit of the called key telephone station is connectedto the ringing tone transmitter circuit RT (FIG. 5) through the line RLof FIG. 5, provided that the telephone line circuit of the called keytelephone station is not busy. For instance in FIG. 5, a switch CN₆ isclosed and the called subscriber key telephone station ST₁ is connectedto the ringing tone transmitter circuit RT. AT the same time, both theinformation which indicates that the intra-office line is being calledand the information which commands the throw-in of the amplifier powersource are set in an outgoing sender register OSR of FIG. 6, so thatsuch information is transferred from the gate circuit GC (FIG. 6) to theinformation lines P₀ and P₁ (FIGS. 3 and 6) connected to the switchingnetwork circuit SNW of FIG. 3. Then, the aforesaid information isconverted into bipolar pulses by the data driver CD₁ of FIG. 3. Thebipolar pulses thus converted are applied to the flip-flops F/F1 andF/F2 and the shift register SR₃ of the key telephone station ST throughthe data receiver circuit CR₂ thereof, as seen in FIG. 8. The flip-flopF/F2 throws in the power source to the amplifier AMP, so that the loudspeaker radiates the ringing tone. Simultanously, the shift register SR3of FIG. 8 flickers the intra-office receiving lamp of the called lampPLP (FIG. 9), so as to indicate that an intra-office call is being madeto the key telephone station ST. In response to the ringing tone, thecalled subscriber raises the handset H and hears the dial tone in thesame manner as the aforesaid originating call. Then he pushes theintra-office receiving button, INTR of FIG. 9. When the informationoriginated by the intra-office receiving button INTR is applied to thereceiving register RCR of FIG. 6, the control circuit CONT of FIG. 6searches, by using the memory RAM, the intra-office circuit IC which isused for the call of said called key telephone station. Then, theinformation relating to which intra-office circuit IC is used for thecall of said called key telephone station, is applied to the shiftregister SR₁ of the switching network circuit SNC of FIG. 3. Thisinformation actuates a switch of that intra-office circuit link. Forinstance, a switch CN₇ of FIG. 5 is closed and then the calling partyST₀ and the called party ST₁ are connected through the intra-officecircuit link ICL₀ by way of the switches CN₄ and CN₇, to allowconversation between these two parties. Thus, an intra-office speechpath is obtained.

When the subscriber wants to originate a line circuit call or to receivea line circuit call, he first raises the handset H and at that time thehandset H actuates the hook switch up, and then he makes sure that thereis a dial tone. Then, he specifies the line circuit number, e.g., one ofthe two digits 10 through 29 of FIG. 9, by dialing the push buttons.After that, the counter circuit COU (FIG. 6) counts the pulse signalswhich are provided in accordance with the dial information and, as aresult, the specified line circuit is connected to both the registerconnecting circuit RGC and the switching network circuit SNC, in thesame manner as the aforesaid connection of the intra-office circuit. Thedial tone disappears in response to the first digit of the dialing, andthe PB signal tone, which is dialed by the subscriber, is transferred tohim, for instance to his key telephone station ST₀ through the registerlink RL₀ of FIG. 5. Upon completion of dialing the two digits of thedialing, e.g., the digits 1 and 0 (shown as 10 in FIG. 9), the switcheswhich have to be closed, are switched from the switches CN₁ and CN₂ tothe switches CN₈ aND CN₉, so that the connection to the privateautomatic branch exchange is accomplished through the line circuit linkLCL₀. In the case of an originating a call, the key telephone stationnumber of the called subscriber is dialed. Then, the PB oscillatorcircuit PBOSC of FIG. 6 sends out the PB signal tone according to thedialing to both the private automatic branch exchange and the keytelephone station. In the case of receiving a line circuit call, thecounter circuit COU (FIG. 6) is reset. Thus. the speech-path iscompleted for allowing conversation between the calling intra-officecircuit party and the called line circuit party. An option circuit OPC,which is included in the common controller CC (FIG. 6), facilitates forinstance abbreviated dialing, 3-digit long line restriction control,simultaneous paging, or the like.

The key telephone system can be provided not only for the usualcommunication of conversation based on the aforesaid new services, butalso for data communication based on the data processing services. Itshould be noticed that the data communication is operated withoutinterrupting the operation of the conversation communication. As can beseen from FIG. 7, in the present invention, a certain time-slot is givento each key telephone station ST₀, ST₁, ST₂ . . . STn, and each keytelephone station is scanned for 500 μs every 40 ms, when n number ofkey telephone stations (n ≦ 80) are scanned, so as to exchange controldata through control lines between the key telephone station and thesubscriber central equipment CE. It should be noted that each controlline CL of FIG. 2 is held idle except during the scanning period of 500μs. Therefore, each control line CL being held idle can be utilized fordata processing. Consequently, if a device for data exchange isinstalled at each key telephone station side and if a data processingunit is installed at the key telephone exchange side, it will becomepossible to exchange a relatively large amount of data between onedevice for data exchange and the other device for data exchange orbetween one device for data exchange and the data processing unit.

An arrangement for fulfilling the aforesaid data processing will now bedescribed by referring to FIGS. 10, 11, 12 and 13. In FIG. 10, the keytelephone station ST, the switching network circuit SNC, the linecircuit LC and the common controller CC, are the same as those shown inFIG. 2. Symbol TAM represents a data terminal equipment and CPUrepresents a central data processing unit.

In addition to the aforesaid 500 μs scanning timeslot, which is referredto as the first time-slot, for each of the key telephone stations (ST₀,ST₁ . . . STn), a second scanning time-slot is provided for each keytelephone station. This second scanning time-slot is used for scanningthe data terminal equipments, so as to enable the exchange of a largeamount of data.

FIGS. 11 and 12 illustrate details of the means for realizing the dataexchange in the aforesaid second time-slot. FIG. 11 is a block diagramshowing modification of the switching network circuit shown in FIG. 3,which further includes a part of the data exchange device. The data gatecircuit DG, the data driver circuit CD₁, the data receiver circuit CR₁,the shift register SR₁, the balance-unbalance converter circuit BUC andthe connecting network CNW of FIG. 11, are the same as those of FIG. 3.Symbol CIR which represents a portion surrounded by a chain line in FIG.11, is a data isolator for separating first data which are handled inthe first time-slot for the usual conversation communication, fromsecond data which are handled in the second time-slot for the datacommunication. The data to be handled in the first timeslot are appliedto the information lines P₀ and P₁, and the signal representing thefirst time slot is applied to the information line S₀. Statusrepresenting signals of the line circuit and the intra-office circuitnecessary for the conversation communication, are delivered through theinformation lines P₀ and P₁ in the first time-slot. On the other hand,the signal representing the second time-slot is applied to theinformation line S₁, and the data necesary for data processing in thesecond time-slot, are applied through the information lines P₄ and P₅.

FIG. 12 is a block diagram showing a modified key telephone station ofFIG. 8 which includes a part of the data exchange device. The symbolsLCR₂, CD₂, SR₂, SR₃, F/F1, F/F2, AMP and SP of FIG. 12, represent thesame means as those of the same symbols of FIG. 8. A counter CAN countsthe time-slots and a symbol COR which represents the portion surroundedby the chain line in FIG. 12, is an or-circuit which separates the datain the first time-slot from the data in the second time-slot, whereinthe counter CAN and the or-circuit COR constitute a data isolator.

The data from the common controller CC (FIGS. 6 and 10) and the centraldata processing unit CPU (FIG. 10) are transmitted through the switchingnetwork circuit SNC (FIG. 11) and are applied to the data receivercircuit CR₂ of the key telephone station ST (FIG. 12). The counter CAN(FIG. 12) detects whether the data received by the data receiver circuitCR₂ (FIG. 12) belong to the first time-slot or the second time-slot. Thedata belonging to the first time-slot are applied to the shift registerSR₃ (FIG. 12) and the contents of the received data are displayed by asuitable lamp L (FIG. 12). The data belonging to the second time-slotare delivered to a data terminal equipment TMA (FIG. 13) throughinformation lines U₀ and U₁ (FIGS. 12 and 13).

The push-button dial signal information or similar information is storedin the shift register SR₂ (FIG. 12). This push-button dial signalinformation or similar information is sent to the subscriber commonequipment CE (FIGS. 2 and 10) by the data driver circuit CD₂ during thefirst time-slot. The data from the data terminal equipment TAM (FIG. 13)are applied to the key telephone station ST through the informationlines U₂ and U₃ (FIGS. 12 and 13), which data are then sent to thesubscriber common equipment CE (FIGS. 2 and 10) during the secondtime-slot.

FIG. 13 is a block diagram of a data terminal equipment according to thepresent invention. In FIG. 13, the data which is delivered through theinformation line U₁ (FIGS. 12 and 13), are applied to the shift registerSR₄ (FIG. 13) in synchronization with clock pulses. The clock pulses areseparated from the aforesaid data and applied to the clock terminal CL(FIG. 13) of the shift register SR₄ through the information line U₀. Thedata stored in the shift register SR₄, are comprised of data informationto be stored in a memory MEM through the lines D₀ . . . Dn (FIG. 13) andaddress information with which said data information is stored in thememory MEM. The address information is delivered through the lines A₀ .. . An (FIG. 13). The data information thus stored in the memory MEM isdisplayed on a terminal display TD (FIG. 13).

The data provided by the data terminal equipment TMA, are applied to ashift register SR₅ (FIG. 13) by pushing appropriate buttons BT (FIG.13). The data which are provided by pushing the buttons BT, are storedin parallel to the shift register SR₅ by the first clock pulse of saidclock pulses provided through the information line U₀ and a flip-flopF/F3. Then synchronized with the second and after clock pulses of saidclock pulses the data are shifted in the shift register SR₅.Accordingly, the output of the flip-flop F/F3, controls the data so asto store it in parallel to the shift register SR₅, to shift the data inseries in the register SR₅ and send it out therefrom. Thus, the datafrom the data terminal equipment TMA are sent to the subscriber commonequipment CE (FIGS. 2 and 10) through a information line U₃ (FIG. 13).An information line U₂ delivers clock pulses of the data stored in theshift register SR5.

The data isolator COR shown in FIG. 12 can be mounted in the dataterminal equipment TMA (FIG. 13). Further, the data isolator CIR shownin FIG. 11 can be mounted in the key telephone station ST or the dataterminal equipment TMA.

As is apparent from the foregoing disclosure, according to the presentinvention, since the selection of a line circuit is performed bypush-button dialing, the number of function buttons is reduced and thesize of the key telephone station is made smaller while simplifying theoperations for various services. Moreover, since a PB oscillator isdisposed within a common controller CC, the conventional PB receiver canbe eliminated from a key telephone system. Certain modifications, suchas a change of telephone number, a change of station data and anaddition of service function, can be accomplished by modifying thecommon controller CC alone, and the number of connecting wires betweenthe subscriber common equipment CE and each key telephone station isreduced to a few wires, whereby installation and maintenance can begreatly simplified.

Furthermore, it becomes possible to provide a wide variety of dataservices at a low cost by using a number of divided time slots on thedata line and by providing data terminal equipment to be served by suchdivided time slots.

The control of the common controller CC is not restricted to the storedprogram type, but the wired logic type control can be used in the commoncontrol CC. When the data transmission system according to the presentinvention is to be applied to a private automatic branch exchange(PABX), the central controller of the PABX may also be used forcontrolling the common controller of the data transmission system, so asto simplify the common controller CC.

What is claimed is:
 1. A key telephone system for subscriberscomprising: a .Iadd.plurality of .Iaddend.key telephone .[.station.]..Iadd.stations .Iaddend.(ST) .Iadd.each .Iaddend.having indication lamps(for example, LP, PLP, OPBL) which indicate the status of .[.the.]..Iadd.each .Iaddend.key telephone station, and a plurality of functionbuttons (for example, OPB, PB, HLD, INTR, INTO): a subscriber commonequipment (CE) which is comprised of a plurality of connecting networkcircuits (for example, CNW₀, CNW₁ . . . CNWn), line circuits (LC),intra-office circuits (IC) and a common controller (CC) which controlssaid connecting network .[.cicuits,.]. .Iadd.circuits, .Iaddend.linecircuits and intra-office circuits, where said connecting networkcircuits connect a speech line (SL) of one key telephone station and aspeech line (SL) of the other key telephone station by using a registerconnecting circuit (RGC) and switching network circuits (for example,SNC₀, SNC₁ . . . SNCn), each of which switching network circuitscooperates with both line circuit links (for example, LCL₀, LCL₁ . . .LCLn) and intra-office circuit links (for example, ICL₀, ICL₁ . . .ICLn); and control lines (CL) which connect each of said key telephonestations and said subscriber common equipment, wherein a desired one ofsaid line circuit links is caught .[.by dialing a desired line circuitnumber by push button means (PB) of said common controller.]. .Iadd.bymeans of said common controller when dialing a desired line circuitnumber by using push buttons (PB), .Iaddend.which desired line circuitnumber is indicated on said indication lamp (LP), while the desired oneof said intra-office circuit links is caught by pushing a desiredintra-office button (for example, INTR. INTRO), by means of said commoncontroller.
 2. A key telephone system for subscribers as set forth inclaim 1, further including: .[.a.]. data terminal .[.equipment.]..Iadd.equipments .Iaddend.(TAM) located on said key telephone stationside; a .[.first.]. data separator (CAN) and a .[.second.]. dataseparator (COR) .[.which are inserted in.].for connecting both said keytelephone station (ST) and said data terminal equipment (TAM) with eachother by way data control lines (CL') .[.between said key telephonestation.]. .Iadd.; .Iaddend.and .Iadd.a data separator (CIR) forconnecting both .Iaddend.said common controller (CC) .[.; a third dataseparator (CIR) which is inserted in.]. .Iadd.and a central dataprocessing unit (CPU) with each other by way of .Iaddend.data controllines (CL") .[.between said common controller and a central dataprocessing unit (CPU).].; wherein data relating to said key telephonestation are transmitted through said control lines (CL) during a firsttime-slot by way of said .[.first, second and third data isolators.]..Iadd.data separators (CAN), (COR) and (CIR), .Iaddend.and data relatingto said data terminal equipment are transmitted through both saidcontrol lines (CL) and said data control lines (CL', CL") during asecond time-slot by means of said .[.first, second and third dataisolators.]. .Iadd.data separators (CAN), (COR) and (CIR), .Iaddend.anddata relating to said data terminal equipment are transmitted throughboth said control lines (CL) and said data control lines (CL', CL")during a second time-slot by means of said .[.first, second and thirddata isolators.]. .Iadd.data separators (CAN), (COR) and (CIR),.Iaddend.whereby data transmission is effected between one of said dataterminal equipments and .[.the other.]. .Iadd.another .Iaddend.of saiddata terminal equipments and between one of said data terminalequipments and said central data processing unit during said secondtime-slot.